How to compress a PDF to 100KB without ruining quality

A practical guide to PDF compression: what actually shrinks files, the tradeoffs, and a free browser-only tool that does it well.

Email rejected your attachment. Job application demanded a 2 MB PDF. WhatsApp won't let you forward that scan. The cause is always the same: someone, somewhere, set a file size limit and your PDF is over it.

Good news: most PDFs can shrink to a quarter of their size with no visible quality loss. The trick is knowing what's making the file big in the first place.

What actually takes up space in a PDF

Three things, in order of typical contribution:

Embedded images. A 10 MB scanned PDF is almost certainly storing each page as a high-resolution photograph. Image downsampling and recompression is where the real wins live.
Embedded fonts. Branded PDFs often carry the entire glyph set of a custom font for every page. Font subsetting (only embedding the characters actually used) cuts this dramatically.
Stream filters and metadata. Object stream compression, removing thumbnails, dropping XMP metadata — each shaves 1-5%.

Pure text PDFs (a Word export, for instance) usually compress modestly — there's just not much fat to trim. PDFs with photos, scans, or screenshots are where you can shrink by 50-90%.

The three compression strategies

1. Lossless — re-save with optimal settings

Object stream compression, removing duplicate resources, dropping thumbnails. Saves 5-15% on most files. No visible change. This is what most "compress PDF" tools do at their lightest setting.

2. Lossy image recompression

Embedded JPEGs are re-encoded at lower quality, embedded PNGs are downsampled. The page text and vector graphics stay sharp, only the photographic content loses fidelity. For a typical scan-heavy PDF, 50-75% smaller. For a screenshot-heavy PDF, even more.

3. Page rasterization

Each page is rendered as an image, then re-embedded as a single compressed JPEG. The most aggressive option — even text becomes a picture, so it can no longer be selected or searched. Use only when size matters more than functionality, like sending an archival copy over a slow connection.

Picking the right strategy for your file

Word/Pages export. The lossless re-save is your friend. Don't expect miracles.
Scanned document. Lossy image recompression at medium quality. You'll keep readability and the file shrinks dramatically.
PDF with screenshots. Same — lossy with quality ~80%. Test both medium and aggressive presets to find the sweet spot.
Archival copy where size is everything. Rasterize. Accept the loss of selectable text and OCR.

How to compress a PDF in your browser

Most online compressors upload your file. If you're sending a contract, a tax return, or anything with personal info, that's the wrong default.

Our compress-PDF tool runs entirely in your browser. Three quality levels: Recommended (best balance), Strong (smaller), Extreme (smallest possible). It shows the before-and-after size so you can see exactly what you saved.

Tips for shrinking a PDF further

Delete pages you don't need. Use our delete-pages tool to drop covers, blank pages, or duplicates before compressing.
Crop wide margins. Crop the PDF to remove white space around the content — when combined with rasterization in the compress step, it removes empty pixels too.
Convert to images then back. Use PDF to JPG, then JPG back to PDF. This is what rasterization does internally — sometimes manually controlling the quality slider gives you a smaller file.

What about 100KB?

100KB is genuinely small. For a one-page PDF with mostly text and a small logo, a Strong compression typically lands in the 50-150KB range. For a multi-page scanned PDF, hitting 100KB usually means Extreme rasterization with aggressive quality settings — and the result will look noticeably softer.

If 100KB is a hard requirement (a job application, say), consider rebuilding the document instead: paste the content into a fresh Word doc, export as PDF with "minimum size" settings, and the result will often be tens of KB.

Final checklist

Use a browser-only tool to keep your file private.
Pick the lightest preset that meets your size target.
Delete unused pages and crop margins first.
Rasterize only as a last resort.